Photomicrograph of the histopathology in an acute case of gonococcal urethritis (bacteria are small dots, many of which are inside polymorphonuclear neutrophils). (Photo credit: CDC/ Joe Millar)

The transfer of genes from one species to another, a process known as horizontal (or lateral) gene transfer, is a unique mechanism by which many single-celled organisms adapt and evolve. And according to new research led by Mark Anderson, a postdoctoral fellow at Northwestern University in Chicago, it seems that certain bacteria that call our bodies home have benefited from the acquisition of human DNA.

In fact, Anderson and colleagues, in the journal mBio, have provided the first evidence for horizontal gene transfer between human and bacterial cells. The lucky bacterial recipient of human DNA is none other than Neisseria gonorrhoeae, the organism that causes gonorrhea. And, as luck would have it, the human DNA acquired by this organism may have facilitated its adaptation to the tissues of the human genital tract.

Gene transfer is suspected to be a common occurrence among single-celled organisms, such as bacteria and the primitive archaea, and even among bacteria and more complex organisms, such as protozoans. For many years, human cells were believed to be capable of participating in the transfer of genetic material with other species, though there was little evidence to support this hypothesis.

The organisms most likely to trade genes with our cells are bacteria, a few trillion of which are present on and in our bodies. Gene transfer with N. gonorrhoeae became suspect after the researchers sequenced the DNA of organisms from patient samples and found that the bacterial DNA sequence contained a segment identical to an element of DNA found in the human genome. About 11 percent of the sequenced samples of gonorrhea contained the human DNA sequence. When bacteria closely related to N. gonorrhoeae were analyzed, the researchers did not find any trace of the human DNA, indicating that the gene transfer happened fairly recently in organism’s evolution.